This invention involves a process for making amines, specifically monomethylamine and dimethylamine, in which methanol and/or dimethylether and ammonia are contacted in the presence of a zeolite catalyst.
Methylamines are generally prepared in industrial quantities by continuous reaction of methanol and ammonia in the presence of a silica-alumina catalyst. The reactants are typically combined in the vapor phase, at temperatures in the range of 300.degree. C. to 500.degree. C., and at elevated pressures. Trimethylamine is the principal component of the resulting product stream, accompanied by lesser amounts of monomethylamine, and dimethylamine. From a commercial standpoint, the most valued product of the reaction is dimethylamine, in view of its widespread industrial use as a chemical intermediate. Accordingly, a major objective of those seeking to enhance the commercial efficiency of this process has been to improve overall yields of dimethylamine and monomethylamine, relative to trimethylamine. Among the approaches taken to meet this objective are recycling of trimethylamine, adjustment of the ratio of methanol to ammonia reactants and use of selected dehydrating or aminating catalyst species. Due to the commercial importance of the process, quite a number of patents and technical contributions to the literature have resulted. Those most relevant to the present invention are summarized below.
Gier et al., U.S. Pat. No. 4,602,112, disclose a process for producing dimethylamine comprising reacting methanol and/or dimethylether and ammonia in amounts sufficient to provide a C/N ratio from about 0.2 to about 1.5, at a temperature from about 250.degree. C. to about 450.degree. C., in the presence of a catalytic amount of an acidic H--ZK-5 zeolite derived from K, Cs--ZK-5 catalyst.
Gier et al., U.S. Pat. No. 4,806,689, disclose a process for producing dimethylamine, as described above, in the presence of a catalytic amount of an acidic zeolite rho.
Abrams et al., U.S. Pat. No. 4,814,503, disclose an improvement to Gier's '689 process (above) through the use of catalyst zeolite rho, zeolite ZK-5 or a combination thereof, calcined in the presence of steam and/or ammonia, which improves catalyst selectivity to dimethylamine and catalyst activity.
Kerr, U.S. Pat. No. 3,247,195, first discloses the composition and method of preparation of zeolite ZK-5, prepared from mixtures of oxides Na.sub.2 O, Al.sub.2 O.sub.3, [(CH.sub.3).sub.2 (CH.sub.2 CH.sub.2).sub.3 N.sub.2 ]O, SiO.sub.2, and H.sub.2 O, and identified by its X-ray diffraction pattern.
Robson, U.S. Pat. No. 3,720,753, discloses a preparation of zeolite ZK-5 prepared from K and Cs. Robson, U.S. Pat. No. 3,904,738, discloses a preparation of zeolite rho.
Shannon et. al., Journal of Catalysis 115 (1989) describes the physical and catalytic properties of ZK-5 catalysts prepared by deep-bed and shallow-bed calcination techniques and the effect on selectivity.
Verduijn, U.S. Pat. No. 4,994,249, discloses a preparation of ZK-5 having a SiO.sub.2 /Al.sub.2 O.sub.3 ratio of up to 10 prepared by the use of potassium and strontium in the synthesis gel, which was found to be useful as a catalyst in hydrocracking, reforming and for separations.
As the foregoing discussion suggests, new process improvements which suppress production of trimethylamine and optimize dimethylamine and monomethylamine yields are of significant interest to the chemical industry.